One day my new MacBook Pro 17″ wouldn’t wake up. When I opened the lid machine was running but the Desktop wouldn’t load (just a default blue Desktop background colour) and there was no response from the Mouse or Keyboard. I eventually had to hard reset the Mac.
This annoying issue can apparently be caused a few different ways, but if your Mac is new and has all System Updates applied, chances are that the issue is caused when you close the lid and then move the mac before the contents of RAM are written out. There’s a feature called Safe Sleep, enabled by default, which can preserve and restore the state of a sleeping Mac even when the battery is removed. This sounds great, but the Safe Sleep procedure can take up to 30 seconds, which is too long for me.
How to fix this annoying problem? Here’s how I switched it off:
sudo pmset -a hibernatemode 0 sudo rm /var/vm/sleepimage
…you need to supply the super user password. After making the change, reboot the Mac. The Mac should now Sleep within a couple of seconds. The second line removes the file that Sleep Safe uses to store the contents of RAM. Since you’ve switched off Safe Sleep, the space can be recovered.
Personally I don’t see the need for Safe Sleep on a Mac with a non-removable battery, but be aware that if the machine is asleep and runs out of battery power you wil lose your logged in session! I haven’t tried it, and most OS X apps will deal pretty well with this anyway, but it’s not wise to let this happen…